1. Field of the Invention
This application is related to co-pending U.S. Ser. No. 08/585,026 entitled "Variable Stiffness Bushing Using Magnetorheological Elastomers" filed Jan. 11, 1996, and incorporated herein by reference, co-pending U.S. Ser. No. 08/585,069 entitled "Method and Apparatus for Varying the Stiffness of a Suspension Bushing" filed Jan. 11, 1996, and co-pending U.S. Ser. No. 08/681,424 entitled "Method and Apparatus for Reducing Brake Shudder" filed Jul. 23, 1996. This invention relates to a method for evaluating chassis elastomeric devices used in motor vehicles. More particularly, the method are useful for rapidly evaluating different physical properties of chassis elastomer devices by using magnetorheological elastomers to rapidly change the physical properties of the subject elastomeric device during evaluation.
2. Disclosure Information
Vehicle ride and handling performance are strongly influenced by the operative characteristics of the various bushings utilized within the automotive vehicle suspension system. Changes in the spring rate, or stiffness, dampness values of a particular bushing can directly influence a variety of operating characteristics, such as vehicle understeer, oversteer, squat and dive characteristics, as well as chassis noise, vibration, and vehicle ride harshness.
For instance, it has been observed that varying the stiffness of suspension bushings on a driven axle can significantly improve the ride and shift quality as perceived by an operator. Similarly, softening control arm inner bushings can improve noise, vibration and harshness qualities while possibly negatively impacting the vehicle's handling and dynamics capabilities. Generally speaking, optimal ride quality demands a suspension bushing having a relatively low spring rate. This permits the suspension to absorb disturbances in the roadway, such as tar strips, chuck holes, etc., without transmitting jarring vibrations to the occupants of the vehicle. On the other hand, optimal handling and dynamics characteristics, including braking demands a bushing having a relatively high stiffness. The "correct" bushing represents acceptable performance in all of the vehicle performance attributes established for the particular car. Finding the "correct" bushing is accomplished through a time consuming and costly process of trial and error.
For instance, in connection with the set-up and calibration of automotive vehicle suspension systems, the spring rates of the bushings are determined through this lengthy trial and error process. Generally, this includes fabricating bushings possessing what are believed to be the correct physical characteristics. The suspension is disassembled and the bushings are installed. The vehicle is evaluated and directional changes are made based on the performance of these bushings in the vehicle. The next iteration bushings are installed, and if all is well, they work. In fact, what often happens is the one set of bushings solves one issue, but creates a new issue somewhere else in the system. These "system" interactions can force the process through several time consuming and costly iterations, changing many of the elastomeric devices on the vehicle several times.
It would be desirable to overcome the aforenoted difficulties with tuning elastomeric devices for use in motor vehicles by providing a method for rapidly evaluating the physical properties of chassis elastomeric devices.